Chronic total occlusion of a blood vessel is, as the name suggests, a condition in which there is complete (or near complete) obstruction of that vessel due to the development of an intravascular lesion comprising atheromatous plaque material and/or thrombic material. Between 10 and 20 percent of patients undergoing percutaneous coronary interventions (PCI) have CTO. Successful opening of CTO lesions improves anginal status, increases exercise capacity, and reduces the need for bypass surgery. However, PCI of cases of CTO have historically posed problems, with lower success rates (40 to 80 percent-average 60 percent), higher equipment costs, and a higher restenosis rate. When MACE (Major Arterial or Cardiac Events) is taken into account, the success rate typically in the range of 20 to 30 percent.
Conventional intervention tools such as angioplasty balloons are often too flexible or blunt to cross highly stenosed lesions such as CTOs, which often contains extremely hard, calcified tissue that may form an impenetrable barrier to the advancement of a guidewire therethrough. Even a less stenosed lesion may contain complex structures which may trap or divert the steering end of the guidewire. In view of the great difficulties encountered in attempting to properly position a guidewire across the stenosis, conventional guided atherectomy or dilatation devices such as cutting elements and balloons cannot be used to cross the lesion as long as a guidewire was not inserted through the lesion since they rely on complete wire crossability.
A further problem associated with the use of conventional devices is the risk of perforating the blood vessel being treated. For example, a guidewire or cutting tool, when advanced, may cause dissection of the tissues of the arterial wall instead of the occlusion, thereby creating a false lumen and possibly perforating the artery. If enough blood from a perforated artery accumulates in the pericardial space surrounding the heart, it will result in a condition known as cardiac tamponade in which the heart is compressed and emergency surgical intervention is required to avert heart failure and death.
Another reason that conventional types of apparatus are typically ineffective in treating total or near total occlusions is that conventional balloon catheter shafts and guidewires do not perform well under the compressive loading and torque loading that are required in order to advance such devices across a CTO lesion.
Statistically, the predominant reason for failure to open CTO lesions with PCI has been failure to cross the lesion with a guidewire (80 percent) and failure of a balloon to track along the guidewire (15 percent) through the very hard lesion. Many types of guidewires and devices have been tried, but successful recanalization has remained at about 60 percent. Crossing CTO lesions in patients with peripheral vascular disease has met with similar problems, for example, the reported success rate for percutaneous catheter-based treatment of chronic subclavian artery occlusion being in the range of 46%-83%.